A liquid crystal (LC) television includes a liquid crystal display (LCD) panel and a backlight unit, and the backlight unit usually uses a light emitting diode (LED) as a backlight source, where a plurality of LED lamps are connected in series to form an LED light bar driven to display by a backlight driving circuit. An LCD television, having a large size display panel, correspondingly requires a high backlight brightness, and needs a plurality of LED light bars that are connected in parallel, thus output power of an entire backlight unit is great; however, the backlight driving circuit using a single boost circuit does not provide a enough power, and uses two boost circuits to drive the plurality of LED light bars, where the two boost circuits are connected in parallel. As shown in FIG. 1, an external power source V+ is received by a first boost circuit 21 and a second boost circuit 22, which together drive the LED light bars 30. The first boost circuit 21 drives the LED light bars 30 through a first constant current driving chip 11, the second boost circuit 22 drives the LED light bars 30 through a second constant current driving chip 12.
Transfer efficiency of the boost circuit is the greatest in a full load working status. As the output power reduces, the transfer efficiency of the boost circuit reduces. Thus, when the first boost circuit 21 and the second boost circuit 22 simultaneously work in a light load status, heat loss of an entire backlight driving circuit is great, and transfer efficiency of two boost circuits is smaller than the transfer efficiency of signal boost circuit which works in the full load working status.